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A symbol is a waveform, a state or a significant condition of the communication channel that persists, for a fixed period of time. A sending device places symbols on the channel at a fixed and known symbol rate, and the receiving device has the job of detecting the sequence of symbols in order to reconstruct the transmitted data. There may be a ...
However, in specifications for TDMA systems such as GSM, the guard period is defined as being at the end of the timeslot. Longer guard periods allow more distant echoes to be tolerated but reduce channel efficiency. For example, in DVB-T, guard intervals are available as 1/32, 1/16, 1/8 or 1/4 of a symbol period. The shortest interval (1/32 ...
The unit interval is the minimum time interval between condition changes of a data transmission signal, also known as the pulse time or symbol duration time.A unit interval (UI) is the time taken in a data stream by each subsequent pulse (or symbol).
And because the shortest decodable transmission is one TTI the shortest period over which BER can be estimated is also one TTI. Thus in networks with link adaptation techniques based on the estimated BER the shortest interval between reports of the estimated performance, which are used to adapt to the conditions on the link, is at least one TTI.
The figure shows how a spread-spectrum signal is generated. The data signal with pulse duration of (symbol period) is XORed with the code signal with pulse duration of (chip period). (Note: bandwidth is proportional to /, where = bit time.)
However, in practice, this cannot be achieved, as real signals are always time-limited. So, to mimic the infinite behavior, prefixing the end of the symbol to the beginning makes the linear convolution of the channel appear as though it were circular convolution, and thus, preserve this property in the part of the symbol after the cyclic prefix.
If the symbol duration is long enough compared to the delay spread (typically 10 times as big would be good enough), one can expect an equivalent ISI-free channel. The correspondence with the frequency domain is the notion of coherence bandwidth (CB), which is the bandwidth over which the channel can be assumed flat (i.e. channel that passes ...
The LTE services were launched by major North American carriers as well, with the Samsung SCH-r900 being the world's first LTE Mobile phone starting on September 21, 2010, [11] [12] and Samsung Galaxy Indulge being the world's first LTE smartphone starting on February 10, 2011, [13] [14] both offered by MetroPCS, and the HTC ThunderBolt offered ...